Future trends Future trends in stratosphere-to-troposphere transport in stratosphere-to-troposphere transport

in CCMI modelsin CCMI models

Marta Abalos (Universidad Complutense de Madrid), Clara Orbe, Douglas E. Kinnison, David Plummer, Luke D. Oman, Patrick Jöckel, Olaf Morgenstern, Rolando R. Garcia, Guang Zeng, Kane A. Stone and Martin Dameris

Workshop: Stratospheric predictability and impact on the troposphereReading, November 2019

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Ozone layer projected to recover in the 21st century

2018 WMO Ozone Assessment Report (Ch. 3)

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Tropospheric ozone: uncertain future evolution

Dohmse et al. 2018 ACP

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posp

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oz

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12 J

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Ozone distribution in the UTLS is important for surface climate

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Combined effects of GHG increase + ODS decrease

Banerjee et al. 2016 ACP

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Goal of this study:

Assess 21st century trends in stratosphere-to-troposphere transport in CCMI models (RCP6.0)

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Goal of this study:

Assess 21st century trends in stratosphere-to-troposphere transport in CCMI models (RCP6.0)

Use artificial tracers to focus on transport changes (not chemistry):

O3S:

Stratospheric ozone, no tropospheric production

st80:Stratospheric passive tracer, fixed above 80 hPa

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Evolution of ozone in the troposphere

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Evolution of stratospheric ozone (O3S) in the troposphere

No changes in tropospheric chemistry

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Evolution of passive stratospheric tracer (st80)

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Stronger climate response → stronger STT increase

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Increase in stratospheric tracer concentrations in the troposphere

Increase in stratosphere-to-troposphere transport

Robust result across models:

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Spatial structure of trends in stratospheric ozone (O3S)

1) Stratospheric trends reveal fingerprint of BDC acceleration

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Spatial structure of trends in stratospheric ozone (O3S)

2) Tropospheric trends mostly positive, peak in the subtropical UT

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Spatial structure of trends in stratospheric ozone (O3S)

3) Most (4/6) models show negative trends around the NH tropopause

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Contributions from ↑GHG and ↓ODS to trends in O3S

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Spatial structure of trends in stratospheric passive tracer (st80)

1) Stratospheric trends not relevant by definition of the synthetic tracer

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Spatial structure of trends in stratospheric passive tracer (st80)

2) Tropospheric trends mostly positive, peak in the subtropical UT

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Spatial structure of trends in stratospheric passive tracer (st80)

3) Most (3/4) models show negative trends around the NH and SH tropopause

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Contributions from ↑GHG and ↓ODS to trends in st80

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Trends in residual circulation streamfunction

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Trends in residual circulation streamfunction

Ozone hole recovery (Polvani, Abalos et al. 2018 GRL)

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Trends in residual circulation streamfunction

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Trends in Transformed Eulerian Mean transport terms for st80

Advection by the residual circulation

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Subtropical maxima in tracer trends linked to enhanced advective transport into the subtropical UT, due to strengthening of BDC

shallow branch + top of Hadley cell

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Negative trends around extratropical tropopause ...

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... disappear in tropopause-relative coordinates → linked to tropopause rise

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STT increases also in middle and high latitudes

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Trends in Transformed Eulerian Mean transport terms for st80

Advection by the residual circulation

Eddy transport

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Tracer trends around extratropical tropopause linked to tropopause rise, STT increases also in middle and high latitudes due to both advective and eddy transport.

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Conclusions

1- Robust increase in stratosphere-to-troposphere transport (STT) across CCMI models

2- Enhanced STT in the subtropics due to stronger advection by BDC and HC with climate change

3- Tropopause rise leads to negative trends in extratropical UTLS, but STT also increases in that region